Campbell Biology 11th edition chapter 23 summary The Evolution of populations PDF

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The Evolution of populations

The biological evolution corresponds to the processes of modification and adaptation of the species over time. The current diversity of living beings is the result of processes of transformation and adaptation of species to various environments, constituting biological evolution. The main idea of biological evolution is that all living beings share the same ancestor. From there, the huge variety of species we found today emerged. It can be said that evolution is the process by which modern organisms evolved from ancient ancestors. Until the mid-nineteenth century, the idea of creationism predominated. According to creationism, the species were created by a divine act remaining unchanged until today.

Beginning in the mid-nineteenth century, the evolutionary theory begins to gain strength. In this context, the ideas of Charles Darwin and Alfred Russel Wallace are the most consistent in explaining the evolution of living beings. Darwin said that living beings, including man, descend from common ancestors, which have changed over time. Currently, the theory of Neo-Darwinism explains the evolution of living beings. She emerged in the twentieth century and represents the union of Darwin's studies, mainly natural selection, with discoveries in the area of genetics, such as Mendel's laws and mutations.

Its starting point is the establishment of the concept of genetic equilibrium independently by the English mathematician GH Hardy, the German physician W. Weinberg early twentieth century, against the critics of Mendelism, according to which the dominant characters must inevitably be increasingly frequent in the population. However, until the 1930’s, geneticists do not employ the concept of population as such and begin to develop concepts that do not refer to individuals but their sets.

Evidence of biological evolution Among the main pieces of evidence of evolution is the fossil record, the adaptation of living beings to their environments and the similarities between species.

A fossil is any vestige of a very old organism that was preserved over the years by natural means. The study of fossils allows reconstructing the image of an already disappeared species and contributes to the study of the evolution of living beings. From the analysis of similarities and differences between species, we can deduce the moment of their appearance and extinction.

Adaptation The adaptation corresponds to the adjustment that all organisms experience concerning the environment in which they live. Adaptations are characteristics maintained in populations or species by natural selection; they have a relative importance in the survival and reproduction of organisms. Examples of adaptation are camouflage and mimicry.

Similarities between species The similarities between various groups of living beings reinforce the idea that they may have a common ancestor during their evolutionary history. Some pieces of evidence are:

Homologous organs They are those with the same embryonic origin and anatomical similarities, but with different functions. The process that originated the homologous organs is called evolutionary divergence.

Analogous organs are those with the embryonic origin and different anatomical structures but those exercise the same function. Similar organs arise through evolutionary convergence.

Vestigial organs They are atrophied organs with no apparent function. An example is a human appendix, which represents a vestige of a bowel compartment that harbored microbes for cellulose digestion in our herbivorous ancestors.

Mechanisms of biological evolution

The neo- Darwinism theory considers the following mechanisms as factors that contribute to evolutionary moving:

Mutations A mutation corresponds to any alteration in the genetic material of an organism that can cause a new characteristic. If this new feature offers some advantage to the individual, the allele (mutation) tends to be preserved by natural selection.

Genetic drift Genetic drift corresponds to a process of random alteration of allelic frequencies of a population. Genetic drift has no predilection for a certain characteristic or adaptation, that is, it does not depend on the beneficial or harmful effects of an allele. The effect of genetic drift is more pronounced in small populations.

Natural selection Natural selection is one of the fundamental mechanisms of evolution. Through it, the individuals most adapted to a certain condition prevail. Thus, they are more likely to survive, reproduce and transmit their characteristics to their descendants. Natural selection can only take place if there are differences in the population. These differences must have a genetic basis; otherwise, the selection is not transferred to the next generation. This aspect is fundamental since there are differences between individuals that can be caused by non-genetic reasons.

On the other hand, the effects of chance are fundamental in genetics. Mendelian genetics introduced the possibility of knowing the probability of having a certain type of offspring of a couple. However, this probability is independent for each of the descendants and the expected proportions are met only in large numbers of individuals. When talking about population genetics, it is inevitable to talk about chance, because it is a fundamental phenomenon in the evolution of small populations....